Generally, some of heat generated at a combustion chamber of an engine is absorbed by a cylinder head, a cylinder block, intake and exhaust valves, a piston, etc.
When temperatures of the constituent components of the engine excessively increase, the constituent components may be thermally deformed, or an oil film of an inner wall of a cylinder may be degraded such that lubrication performance deteriorates, resulting in thermal problems of the engine.
Due to the thermal problems of the engine, abnormal combustion such as combustion failure, knocking, etc. occur, thus a piston may be melted, which may result in serious damage to the engine. Further, thermal efficiency and power of the engine may deteriorate. In contrast, excessive cooling of the engine may cause the power and fuel consumption to deteriorate, and may cause low temperature abrasion of the cylinder, thus it is necessary to appropriately control temperature of the coolant.
In this respect, in a typical engine, a water jacket is provided inside a cylinder block and a cylinder head, and a coolant circulating in the water jacket cools a periphery of a spark plug corresponding to a combustion chamber and metal surfaces such as peripheries of an exhaust port, a valve seat, etc.
However, in the typical engine, since the coolant flowing in according with the order of cylinders is sequentially circulated in the water jacket provided in the cylinder block, portions of the cylinder block corresponding to upper and lower portions of the combustion chamber at which a relative temperature difference is generated are not effectively cooled, such that the cooling of the engine is not entirely sufficient.
In addition, durability of the engine deteriorates due to poor cooling efficiency of the engine, and if a separate cooling jet is provided and a high performance water pump is used in order to prevent the deterioration of the durability of the engine, costs thereof may increase.
Further, when the temperature of the coolant is low, viscosity of engine oil is high, thus as frictional force increases, fuel consumption increases, that is, fuel efficiency deteriorates, while when the coolant temperature is excessively high, since knocking occurs, performance of the engine may deteriorate by adjusting ignition timing in order to suppress the knocking.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.